SANTA ROSA DE OSOS, Colombia — Colombian officials say 10 peasants have been killed by a drug-trafficking paramilitary group in the country’s worst massacre in more than three years.

Authorities said the bloodshed was carried out by a group known as “Los Rastrojos” — The Scraps — who stormed into a farm at around 6 p.m. local time on Wednesday.

The group killed nine men and a woman in the municipality of Santa Rosa de Osos, about 275 kilometers northeast of the capital Bogota, said Santiago Londono, government secretary for Antioquia state.

It’s the first major massacre in Colombia since August 2009 when 12 members of the Awa indigenous tribe were killed in southwestern Narino state. At the time, a prosecutor investigating the case said the killings had been committed by Los Rastrojos.

The group is a violent offshoot of the Norte del Valle cartel involved in drug trafficking, extortion and murder as it competes with other criminal bands that grew out of the far-right militias known as paramilitaries.

Colombian police say the gang, which is thought to have hundreds of members, operates on Colombia’s Pacific coast and along the border with Venezuela.

Antioquia Police General David Guzman said three armed men arrived at the farm around 6 p.m. Wednesday as farm laborers were finishing their day of work picking fruit. They asked the peasants if they were paying an extortion fee. When the peasants said they didn’t know, the men shot them with rifles and handguns and tossed a grenade at them.

“One of the laborers, apparently the foreman, said he didn’t know (of any payment). That’s all they said and they were shot indiscriminately,” Guzman said. “This case has shocked us for the barbaric, brutal way that they murdered these completely innocent people,” he said.

Several leaders of the Rastrojos were captured last week in the area and officials are blaming the group for the latest bloodshed. Authorities have been unable to reach the farm and collect the bodies because of bad weather, said Londono, the government secretary for Antioquia.

Francisco Jair Lopera, the mayor of Santa Rosa de Osos, called the massacre a source of “national shame.”

Lopera said the victims were in their 30s and 40s and that the owner of the farm was apparently being extorted by the paramilitary group.

In a local radio interview, Defense Minister Juan Carlos Pinzon vowed to go after the killers.